This invention relates to a method and a device for attenuating pressure pulses through fluids, in particular for continuous paper web producing machines.
With continuous paper web making machines, e.g. newspaper printing paper making machines, the aqueous suspension for the formation of the web is currently spread or distributed across the draining cloth of the continuous machine by means of an intake tank, which is in turn connected to the slurry epuration system through a feed conduit.
A determining requisite of paper web making is unexceptionable uniformity of thickness in the lengthwise direction of the web. Lack of uniformity or uneveness of the web result, in fact, in irregularities in the course of the following coating process, which reflects, in turn, into further uneven absorption and drying of the ink when printing. The net result is derating of the print quality to sometimes unacceptable limits and attendant waste of an expensive material.
Care is therefore taken to provide the highest possible degree of homogeneity in the aqueous suspension flow already upstream of the intake tank, so as to achieve the highest uniformity in the spreading thereof through the sheet, and as a direct consequence, in the weight per unit area of the paper produced.
The problem outlined hereinabove is further aggravated in the instance of lightweight substance and high production rate.
As an example, with a substance of 30-50 g/m.sup.2 in paper webs produced on continuous machines having an output rate of 900-1,000 m/minute, there occur wrinkle marks due to the tensions originated in the paper sheet by uneven drying of said web through the drying cylinders of the continuous machine owning to uneven thickness.
In the light of the foregoing, it will be appreciated that if to prevent such uneven thickness formations the output rate is brought down to 100-200 m/minute, for example, then this would reflect in a most adverse way on the economy of the production cycle.
During the web manufacturing process, moreover, increased uneven spots in the paper thickness may also lead to the formation of "holes" through the paper web, so that production would have to be discontinued for a while in order to remove the problem. Given the high output rate, it is evident that discontinuing the operation of the continuous machine results in heavy production losses.
In an attempt at obviating the above drawbacks, so-called "expansion chambers" have been used heretofore which are either shunted from the aqueous suspension feed line or inserted, in the capacity of a spillway, directly in the intake tank, such expansion chambers being also called "surge tanks" and "overflow tanks", respectively.
In prior expansion chambers, the aqueous suspension is allowed to expand and reach a higher level each time that it undergoes disturbances of the character of pressure surges in consequence of the unavoidable interference caused by the various components comprised in the hydraulic circuit, such as filters, pumps, stirrers, and the like, located upstream of the feed conduit to the intake tank.
In actual practice, the effectiveness of these devices has shown to be rather low, because said interference actually extinguishes itself inertially by self-dampening.